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Register a new userOver-density of SMGs in fields containing z~0.3 galaxies: magnification bias and the implications for studies of galaxy evolution
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We report a remarkable over-density of high-redshift submillimetre galaxies (SMG), 4-7 times the background, around a statistically complete sample of twelve 250-micron selected galaxies at z=0.35, which were targeted by ALMA in a study of gas tracers. This over-density is consistent with the effect of lensing by the halos hosting the target z=0.35 galaxies. The angular cross-correlation in this sample is consistent with statistical measures of this effect made using larger sub-mm samples. The magnitude of the over-density as a function of radial separation is consistent with intermediate scale lensing by halos of order 7x 10^{13} M_o, which should host one or possibly two bright galaxies and several smaller satellites. This is supported by observational evidence of interaction with satellites in four out of the six fields with SMG, and membership of a spectroscopically defined group for a fifth. We also investigate the impact of these SMG on the reported Herschel fluxes of the z=0.35 galaxies, as they produce significant contamination in the 350 and 500-micron Herschel bands. The higher than random incidence of these boosting events implies a significantly larger bias in the sub-mm colours of Herschel sources associated with z<0.7 galaxies than has previously been assumed, with f_boost = 1.13, 1.26, 1.44 at 250, 350 and 500-microns. This could have implications for studies of spectral energy distributions, source counts and luminosity functions based on Herschel samples at z=0.2-0.7.
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The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to $zsim8$ to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies ($phi_{rm T}$), more massive than M$_{*} = 10^{6}$ M_0, decreases as $phi_{rm T} sim t^{-1}$, where $t$ is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M$_{*}>10^{7}$ M_0. By using the M$_{*}=10^{6}$ M_0 lower limit we further show that the total number of galaxies in the universe up to $z = 8$ is $2.0^{+0.7}_{-0.6} times 10^{12}$ (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers paradox.
We present the results of a new search for galaxies at redshift z ~ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with H_{160} < 28.6 (AB mag), consider only image regions with an rms noise sigma_{160} > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H_{160} and J_{140}. The result is a survey covering an effective area (after accounting for magnification) of 10.9 sq. arcmin, which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields we confirm the three brightest objects reported by Ishigaki et al. (2014), but recover only one of the four z > 8.4 sources reported by Zheng et al. (2014). In the MACSJ0416.1-240 cluster field we report five objects, and explain why each of these eluded detection or classification as z ~ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ~ 9 galaxies from the previously unsearched MACSJ0416.1-240 parallel field. Based on the published magnification maps we find that only one of these 12 galaxies is likely boosted by more than a factor of two by gravitational lensing. Consequently we are able to perform a fairly straightforward reanalysis of the normalization of the z ~ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star-formation rate density) from z ~ 8 to z ~ 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization.
We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at $z=1.0sim3.2$ with an angular resolution of $sim0.2$. These galaxies were uncovered by the Herschel Lensing Survey (HLS), and feature exceptionally bright far-infrared continuum emission ($S_mathrm{peak} gtrsim 90$ mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5 $mathrm{mu m}$) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small ($R_mathrm{e,dust}/R_mathrm{e,star} = 0.38pm0.14$) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm ($lesssim 0.1$ mJy arcsec$^{-2}$), in which the star formation is distributed over the entire galaxy ($R_mathrm{e,dust}/R_mathrm{e,star}>1$). As a whole, our SMG sample shows a tight anti-correlation between ($R_mathrm{e,dust}/R_mathrm{e,star}$) and far-infrared surface brightness ($Sigma_mathrm{IR}$) over a factor of $simeq$ 1000 in $Sigma_mathrm{IR}$. This indicates that SMGs with less vigorous star formation (i.e., lower $Sigma_mathrm{IR}$) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger $R_mathrm{e,dust}/R_mathrm{e,star}$). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent inside-out quenching, which likely accounts for the emergence of compact quiescent galaxies at $zsim2$.
(abridged) We measure spectral indices for 1823 galaxies in the CNOC1 sample of fifteen X-ray luminous clusters at 0.18<z<0.55, to investigate the mechanisms responsible for differential evolution between the galaxy cluster and field environments. The radial trends of D4000, Hdelta and [OII] are all consistent with an age sequence, in the sense that the last episode of star formation occurred more recently in galaxies farthest from the cluster center. Throughout the cluster environment, galaxies show evidence for older mean stellar populations than field galaxies. From the subsample of galaxies more luminous than M_r=-18.8 + 5log h, we identify a sample of K+A galaxies, which may result from recently terminated star formation. Corrected for a systematic effect which results from the large uncertainties on individual spectral index measurements, we estimate that K+A galaxies make up only 1.5 +/- 0.8 % of the cluster sample, and 1.2 +/- 0.8 % of the field. We compare our data with spectrophotometric models and conclude that up to 1.9 +/- 0.8 % of the cluster population may have had its star formation recently truncated without a starburst. However, this is still not significantly greater than the fraction of such galaxies in the field, 3.1 +/- 1.0 %. Furthermore, we do not detect an excess of cluster galaxies that have unambiguously undergone a starburst within the last 1 Gyr. Our results imply that these cluster environments are not responsible for inducing starbursts; thus, the increase in cluster blue galaxy fraction with redshift may not be a strictly cluster--specific phenomenon. We suggest that the truncation of star formation in clusters may largely be a gradual process, perhaps due to the exhaustion of gas in the galactic disk over fairly long timescales.
Studying the transformation of cluster galaxies contributes a lot to have a clear picture of evolution of the universe. Towards that we are studying different properties (morphology, star formation, AGN contribution and metallicity) of galaxies in clusters up to $zsim1.0$ taking three different clusters: ZwCl0024+1652 at $zsim0.4$, RXJ1257+4738 at $zsim0.9$ and Virgo at $zsim0.0038$. For ZwCl0024+1652 and RXJ1257+4738 clusters we used tunable filters data from GLACE survey taken with GTC 10.4 m telescope and other public data, while for Virgo we used public data. We did the morphological classification of 180 galaxies in ZwCl0024+1652 using galSVM, where 54% and 46% of galaxies were classified as early-type (ET) and late-type (LT) respectively. We did a comparison between the three clusters within the clustercentric distance of 1Mpc and found that ET proportion (decreasing with redshift) dominates over the LT (increasing with redshift) throughout. We finalized the data reduction for ZwCl0024+1652 cluster and identified 46 [OIII] and 73 H$beta$ emission lines. For this cluster we have classified 22 emission line galaxies (ELGs) using BPT-NII diagnostic diagram resulting with 14 composite, 1 AGN and 7 star forming (SF) galaxies. We are using these results, together with the public data, for further analysis of the variations of properties in relation to redshift within $z<1.0$.
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